1. Field of the Invention
The present invention relates to a double sheet feeding detector, a method for detecting double feeding of sheets and a computer program for controlling such a detector, and in particular, concerns a double sheet feeding detector which can more positively detect double feeding of sheets and such a method and a program.
2. Description of the Related Art
When a sheet of paper is fed in a printer, double feeding occurs in the case where two or more sheets are simultaneously fed with at least one portion of one sheet being partially superimposed on another. When such double feeding occurs, it is not possible to carry out a proper printing process. Therefore, in the case where two or more sheets are simultaneously fed, it is necessary to detect this as a double feeding and to temporarily suspend the feeding process.
Conventionally, methods in which ultrasonic waves are used to detect double feeding have been disclosed in Japanese Patent No. 1725105 and JP-A-52-40379.
In Japanese Patent No. 1725105, ultrasonic waves that have been transmitted through sheets are received, and the receiving level is detected. Since there is a difference in the level of the received ultrasonic waves between one sheet of paper and two or more sheets that have been fed, double feeding is detected based upon the difference.
Moreover, as disclosed by JP-A-52-40379, the phase of an ultrasonic wave that has been transmitted through sheets is detected. Since there is a difference in the phase thereof between one sheet of paper and two or more sheets that have been fed, double feeding is detected based upon the phase.
Here, the applicant of the present application has proposed a detecting method in Japanese Patent Application No. 11-13257, in which double feeding is detected by comparing the phases of the receiving signal of an ultrasonic wave and a reference signal, and further comparing a signal corresponding to the phase difference with a reference level.
However, in Japanese Patent No. 1725105, double feeding is detected based upon the receiving level of ultrasonic waves; therefore, in the case when a sheet of paper is thin, there is not much difference in the levels of the received ultrasonic wave signals between one sheet of paper and two or more sheets that have been fed, and it is not possible to detect double feeding correctly.
Moreover, in JP-A-52-40379, in which double feeding is detected based upon the phase of a received ultrasonic signal, when a number of sheets of paper are fed at once, the level of the receiving signal is extremely attenuated, making it impossible to accurately detect the phase of a received signal, and resulting in a failure to accurately detect double feeding.
Furthermore, in the method disclosed in Japanese Patent Application No. 11-13257, since it is necessary to generate a reference signal, a complex process is required in cases when determining conditions, etc. are altered.
The present invention has been devised to solve the above-mentioned problems and to positively detect double feeding independent of the thickness of sheets, and also to easily set determination conditions.
A first double sheet feeding detector of the present invention is provided with: ultrasonic wave generation means for generating ultrasonic waves to be applied to a feeding path for sheets; ultrasonic wave receiving means for receiving ultrasonic waves generated by said ultrasonic wave generation means; phase-difference detection means which detects a phase difference between a phase of the ultrasonic waves received by the ultrasonic wave receiving means and a predetermined reference phase; comparison means which compares the phase difference detected by the phase-difference detection means with a predetermined first reference value that has been preliminarily set; counting means which counts the number of times of cases in which the phase difference, as detected by the phase-difference detection means, exceeds the first reference value based upon the results of comparison of the comparison means; and double feeding detection means which compares the calculated value counted by the counting means with a second reference value that has been preliminarily set, and detects a double feeding of the sheet based upon the results of this comparison.
In this double sheet feeding detector, the number of times of cases in which the phase difference of the received ultrasonic waves from a predetermined reference phase exceeds the first reference value is counted, and a double feeding of sheets is detected based upon the results of comparison between the counted value and the second reference value. Therefore, it is possible to positively detect double feeding independent of the thickness of sheets. Here, the reference phase refers to a phase of a preliminarily set receiving waves that corresponds to the receiving waves obtained when one sheet is being fed.
In particular, since it is not necessary to generate a reference signal to be compared with the received ultrasonic waves, it is not necessary to set and adjust a reference signal so as to detect a double feeding, thereby making it possible to improve the operability.
For example, sheets are made of paper. The ultrasonic wave generating means is provided as an ultrasonic wave transmitter, and the ultrasonic wave receiving means is provided as an ultrasonic wave receiver.
The preliminarily set reference phase of a received ultrasonic wave is digitized as a phase difference with the peak timing of the transmission waves being set as a base point (phase=0). Moreover, the phase of the receiving waves is also measured with the peak timing of the transmission waves being set as a base point (phase=0).
The phase difference detection means may be provided as a CPU.
The counting means may be provided as a determining counter.
The double feeding detection means may be provided as a CPU.
With respect to the first reference value, the comparison means may have at least either a third reference value serving as a reference with respect to the deviation of the phase difference in the positive direction or a fourth reference value having an absolute value different from the third reference value and serving as a reference with respect to the deviation of the phase difference in the negative direction.
The third reference value is formed by, for example, xcex94Z2 shown in FIG. 9, and the fourth reference value is formed by xcex94Z1.
In this manner, by setting the reference values in the positive direction and negative direction as different values, it is impossible to more positively detect double feeding of sheets in response to inherent conditions of respective devices for feeding sheets.
The double feeding detection means may alter the second reference value in accordance with the feeding speed or the size (length) of the sheets.
The second reference value may be set as a small value when the feeding speed of sheets is great, and also set as a great value when the size of sheets is great (the length thereof is long).
In this manner, by altering the second reference value dynamically in accordance with the feeding speed and the size of the sheets, it becomes possible to more positively detect double feeding.
The count number per unit time by the above-mentioned counting means may be altered in accordance with the feeding speed or the size of the sheets.
Thus, it becomes possible to positively detect double feeding.
A feeding means for feeding sheets onto a feeding path may be further placed so that the phase-difference detection means is allowed to detect a phase difference from the reference phase of ultrasonic waves received by the ultrasonic wave receiving means, in synchronism with a motor driving signal.
The feeding means for feeding sheets may be formed by, for example, a motor driver for driving a motor. The signal synchronizing to the feeding amount is formed by, for example, a motor clock synchronous signal.
Thus, even in the case when the feeding speed of sheets is changed in the middle of the feeding process, it is possible to always maintain a predetermined number of phase-difference detections (sampling) with respect to sheets having the same length.
A speed control means, which controls the feeding speed of sheets so as to make the feeding speed of sheets at the time of determination of a double feeding slower than determinations other than double feeding, may be further placed.
The speed control means may be provided by, for example, a motor driver.
By making the feeding speed of sheets at the time of determination of a double feeding slower, it becomes possible to detect a double feeding more accurately.
A level detection means for detecting the level of ultrasonic waves received by the above-mentioned ultrasonic wave receiving means may be further installed, and based upon the results of detection by the level detection means, the double feeding detection means makes it possible to detect a case in which the level of the ultrasonic waves is smaller than the reference value, thus detecting double feeding independent of values of the counted value.
With this arrangement, which is based upon the results of detection by the level detection means, it is possible to detect a case in which the level of ultrasonic waves is smaller than the reference value, thus detecting double feeding independent of values of the counted value; therefore, even when the level of the ultrasonic waves becomes extremely low due to a feeding of a number of sheets at the same time, it becomes possible to accurately detect double feeding.
Moreover, a sheet detection means for detecting the presence or absence of sheets by using the level of a received signal may be further installed.
The sheet detection means may be provided as, for example, a level determining unit.
A level control means, which controls the level of the signal received by the ultrasonic wave receiving means based upon the results of detection by the above-mentioned sheet detection means, may be further installed.
The level control means may be constituted by, for example, analog switches and resistors.
By controlling the level of a received signal based upon the results of detection of sheets, it is possible to set the receiving level in the case of presence of sheets and the level of the receiving signal in the case of absence of sheets to virtually the same level, and consequently to easily carry out signal processing and an accurate double feeding determination process.
A length detection means, which detects the length of sheets based upon the results of detection of the sheet detection means, may be further placed, and the double feeding detection means may detect double feeding of sheets based upon the results of detection by the sheet detection means.
The length detection means may be provided as a CPU.
By detecting double feeding of sheets based upon the results of detection of the length of the sheets, it becomes possible to more accurately detect double feeding.
Based upon the level of the ultrasonic waves received by the ultrasonic wave receiving means, the above-mentioned sheet detection means can detect the presence or absence of sheets.
A correction means for correcting the above-mentioned reference phase may be further installed.
Even in the case when the transmission speed of ultrasonic waves is varied due to environmental variations such as temperature and humidity, it is possible to positively detect double feeding by correcting the reference phase.
The correction detection means may be provided as a CPU.
A memory means, which acquires a first initial phase that is a phase of the ultrasonic waves received by the ultrasonic-wave receiving means and that represents an initial state in which no sheet is present in a detection target area and a second initial phase that is a phase of the ultrasonic wave received by the ultrasonic-wave receiving means and that represents an initial state in which a sheet is present in the detection target area, and stores these, or stores the difference between the first initial phase and the second initial phase, is further installed, and the correction means corrects the reference phase based upon the first initial phase and second initial phase stored in the memory means or based upon the difference thereof.
The memory means may be formed by, for example, a computer memory or the like.
The above-mentioned correction means acquires a phase at the time of correction that is the phase of the ultrasonic waves received by the ultrasonic-wave receiving means during the correcting operation when no sheet is in the detection target area, calculates a correction-difference phase that corresponds to a difference component between the phase at the time of correction and the first initial phase stored in the memory means, and corrects said reference phase to a correction reference phase based upon the second initial phase and the correction difference phase stored in the memory means, or corrects the reference phase to a correction reference phase based upon the phase at the time of correction and a difference between the first initial phase and second initial phase stored in the memory means.
The above-mentioned correction means may multiply the component of a difference between the phase at the time of correction and the first initial phase stored in the memory means by a predetermined coefficient so as to calculate the correction difference phase.
Here, the process for calculating the correction difference phase through the multiplication using the coefficient includes processes for preliminarily storing values multiplied by the coefficient in the memory and for reading the corresponding value.
This process makes it possible to carry out a more accurate correction.
The above-mentioned correction means acquires a phase at the time of correction that is the phase of the ultrasonic waves received by the ultrasonic-wave receiving means during the correcting operation in the case of the absence of a sheet in the detection target area, calculates a correction-difference phase that corresponds to a difference component between the second initial phase and first initial phase stored in the memory means, and based upon the phase at the time of correction and the correction-difference phase, corrects the reference phase to the correction reference phase.
This process makes it possible to carry out a more accurate correction.
The correction means may acquire the phase at the time of correction prior to the start of feeding of the sheets.
The correction means may acquire the phase at the time of correction during a period in which the sheets are successively fed, and in the period in which no sheets are present between one of the sheets fed and the next sheet to be fed.
A calculation means, which calculates the average value of phases of the ultrasonic waves received by the ultrasonic-wave receiving means, is further installed, and the correction means corrects the reference phase based upon the average value calculated by the calculation means.
The calculation means may be provided as, for example, a CPU.
By utilizing the average value in this manner, even in the case when it is difficult to detect the phase of an ultrasonic wave accurately, that is, a case in which the environment is gradually varied during feeding processes of sheets with the distance between feeding processes being short without any sheet coming in between, it becomes possible to detect double feeding accurately. With respect to the average value, not only the average value on one sheet, but also the average value on a predetermined number of sheets of not less than two sheets, may be used. The arrangement makes it possible to reduce such cases as to have a great variation in the reference value due to a sudden variation in the phase.
A transporting plate used for feeding the sheets may have an area having a plurality of small pores formed therein through which the ultrasonic waves are transmitted.
By forming many small pores in this manner, it is possible to prevent the ends of the sheets from coming into contact with the hole and causing a feeding error due to warped sheets. Thus, it becomes possible to positively transmit the ultrasonic waves, and consequently to detect double feeding accurately.
A double sheet feeding detecting method of the present invention includes the steps of: detecting a phase difference of the received ultrasonic waves from a reference phase; comparing the phase difference detected by the phase-difference detection step with a preliminarily set predetermined first reference value; counting the number of times in which the phase difference, detected by the phase-difference detection step, exceeds the first reference value based upon the results of comparison obtained by the comparison processes; and detecting double feeding of sheets by comparing the counted value calculated by the counting step with a second reference value that has been preliminarily set and based upon the results of comparison.
In accordance with this double sheet feeding detecting method, it is possible to obtain the same effects as those obtained by the double sheet feeding detector.
A first program of the present invention, which is a program for controlling a double sheet feeding detector which applies ultrasonic waves onto a transporting path of sheets and receives the applied ultrasonic waves to detect a double feeding of sheets, includes program modules which allow a computer to execute the steps of: detecting a phase difference of the received ultrasonic waves from a reference phase; comparing the phase difference detected by the phase-difference detection step with a preliminarily set predetermined first reference value; counting the number of times in which the phase difference, detected by the phase-difference detection step, exceeds the first reference value based upon the results of comparison obtained by the comparison processes; and detecting a double feeding of sheets by comparing the counted value calculated by the counting step with a second reference value that has been preliminarily set and based upon the results of comparison.
In this case, the respective steps are composed of the same steps disclosed in embodiments of the double sheet feeding detecting method.
Then, by using this program, it also becomes possible to achieve a double sheet feeding detector that can positively detect the double feeding of sheets.
A second double sheet feeding detector of the present invention includes ultrasonic wave generation means for generating ultrasonic waves to be applied to a feeding path for sheets; ultrasonic wave receiving means for receiving ultrasonic waves generated by the ultrasonic wave generation means; phase detection means which detects a phase of the ultrasonic waves received by the ultrasonic wave receiving means; varying amount detection means which detects the varying amount of the phase detected by the phase detection means; accumulation means which accumulates the varying amounts detected by the varying amount detection means; comparison means which compares the varying amount accumulated by the accumulation means with a predetermined reference value preliminarily set; and double feeding detection means which detects double feeding of the sheet based upon the results of comparison of the comparison means.
In this case, the relationship between the ultrasonic wave generation means for sheets and the ultrasonic wave receiving means in embodiments is the same as that of the first double sheet feeding detector.
The phase difference detection means may be provided as, for example, a CPU.
The varying amount detection means may be provided as, for example, a CPU which executes a process for calculating the difference between the phase detected last time and the phase detected this time.
The accumulation means may be provided as, for example, a CPU which carries out a process for adding the varying amount of this time to the current varying amount.
The comparison means may be provided as, for example, a CPU. The double feeding detection means may be provided as, for example, a CPU.
In the second double sheet feeding detector of the present invention, the varying amount of the phase of the received ultrasonic waves is detected, and detection is carried out on a double feeding based upon the results of comparison between the accumulated varying amount and the reference value.
Therefore, it becomes possible to positively detect double feeding independent of the thickness of the sheets. Moreover, it is not necessary to set parameters, etc. so as to detect double feeding, and consequently improves operability.
The number of times of detection per unit time by the varying amount detection means may be altered in accordance with the feeding speed or the size of sheets.
In the comparison means, it is possible to alter the reference value in accordance with the feeding speed or the size of the sheets.
This reference value may be decreased when the feeding speed of the sheets is small, while it may be increased when the feeding speed of the sheets is great.
The setting of the reference value in this manner makes it possible to more accurately detect double feeding.
A speed control means controls the feeding speed of sheets at the time of a double feeding determination so as to be slower than determinations other than double feeding.
A level detection means, which detects the level of a received ultrasonic wave by the above-mentioned ultrasonic wave receiving means, is further installed; thus, the double feeding detection means can detect double feeding of sheets independent of the results of phase detection by the phase detection means in the case when the level detected by the level detection means is smaller than a predetermined reference value.
By detecting double feeding of sheets utilizing the results of detection by the level detection means, it becomes possible to more positively detect double feeding.
Moreover, a sheet detection means, which detects the presence or absence of sheets by utilizing the level of a received signal, may be further installed.
The sheet detection means is formed by, for example, a level determining unit.
A level control means, which controls the level of a signal received by the receiving means based upon the results of detection by the sheet detection means, may be further installed.
The level control means is constituted by, for example, analog switches and resistors.
By controlling the received signal level based upon the results of the detection of the sheets, it becomes possible to process the level of received signals at virtually the same levels as in the cases of the presence of sheets and the absence thereof, and consequently to detect double feeding more accurately.
A length detection means, which detects the length of sheets based upon the results of detection by sheet detection means, may be further provided so that the double feeding detection means is allowed to detect double feeding of sheets based upon the results of detection by the length detection means.
The length detection means is provided as, for example, a CPU.
By further detecting double feeding of sheets based upon the results of detection by the length detection means, it becomes possible to more positively detect double feeding.
The above-mentioned sheet detection means may detect the presence or absence of sheets based upon the level of the received ultrasonic waves by the ultrasonic wave receiving means.
A second double sheet feeding detection method of the present invention includes the steps of: detecting the phase of a received ultrasonic wave; detecting a varying amount of the phase detected by the phase detection step; accumulating the varying amounts detected by the varying amount detection step; comparing the varying amount accumulated by the accumulation step with a predetermined reference value preliminarily set; and detecting double feeding of sheets based upon the results of comparison of the comparison step.
The ultrasonic wave generation step and the ultrasonic wave receiving step are constituted by, for example, processes in which an oscillation amplifier controls an ultrasonic wave transmitter and a process for receiving the generated ultrasonic waves by an ultrasonic wave receiver.
In the second double sheet feeding detection method also, it is possible to obtain the same effects as those obtained in the second double sheet feeding detector.
A second program of the present invention, which is a program for a double sheet feeding detector which applies ultrasonic waves onto a transporting path of sheets and receives the applied ultrasonic waves to detect double feeding of sheets, includes program modules which allow a computer to execute the steps of: detecting the phase of a received ultrasonic wave; detecting a varying amount of the phase detected by the phase detection step; accumulating the varying amounts detected by the varying amount detection step; comparing the varying amount accumulated by the accumulation step with a predetermined reference value preliminarily set; and detecting a double feeding of the sheet based upon the results of comparison of the comparison step.
The phase detection step, the varying amount detection step, the accumulation step, the comparison step and the double feeding detection step of this embodiment correspond to the respective steps in the second double sheet feeding detection method of the present invention.
By using this program also, it becomes possible to achieve a double sheet feeding detector that can positively detect a double feeding of sheets independent of the thickness of sheets.